The Bonn charger (designed by Don
Bonn) is a bad-boy charger with a few manners. The key addition is a big
series inductor, in series with the input to the bridge rectifier. The
inductor filters and limits the peak current, so it won't burn up cords.
The inductor also improves the power factor, so you get more charging current
out of a given AC outlet. It also has a GFCI for safety, an ammeter so
you know what you're doing, and a timer to automatically shut it off.

GFCI = Ground Fault Circuit Interruptor.
This is the same gadget you find in your kitchen, bathroom, or outside
outlets. It is there to prevent shocks if you touch your batteries while
the charger is operating.

S1 = Circuit breaker. I used a 120vac
12amp breaker which looks like an oversized toggle switch. This provides
an easy way to turn the charger on/off. I used a 12amp breaker so it will
trip *before* the 15amp breaker that protects the circuit, so you don't
have to run down to the basement or get someone with a key to reset
a tripped breaker.

S2 = Intermatic 240vac 20amp 12-hour
timer. This is a mechanical timer with a knob that you can set for 0-12
hours. Set it to the maximum charging time to automatically shut off when
done.

S3 = SPDT toggle switch, 120vac
15amp minimum. This switch selects between taps on the inductor, to control
the charging rate. If you can find one, a multi-position rotary switch
can be used instead to select more than 2 taps.

C1 = 5-10uf 220vac or more motor
run capacitor. This must be a film or paper/oil capacitor, not an electrolytic!
It improves the power factor so you can charge at a higher current without
tripping the breaker.

J1 = normal 120vac 15amp receptacle.
This is a "convenience" outlet for plugging in a 12v accessory battery
charger, heater, or other gadget you might need. As shown it is a switched
outlet. If your GFCI includes such a receptacle, you can use it.

J2 = Anderson PowerPole connector,
15/30/45 amp size (all use the same housing). These are DC rated to 600v
and the industry standard for battery connectors.

D1 = bridge rectifier, 400v 35amp
minimum. If you skimp on the ratings, it will fail sooner or later!

You'll probably have to make this
inductor yourself. Find a 60hz transformer of about the right weight, and
take it apart. Rewind it with as much #12 wire as will fit, bringing
out taps every layer or so. Reassemble it with all the "E" laminations
in one stack, and all the "I" in another. Put a thin paper shim between
the E and I stacks (this stabilizes the inductance so it won't change so
much with current). The thickness of this paper shim will adjust the inductance,
too.

You also need a good accurate voltmeter.
The charging current alone is meaningless unless you also know the voltage!
I use the E-meter already in my EV. You could add a cheap digital multimeter
onto the charger, powering it with a "wall wart" so you don't have to keep
replacing the battery.

--Ring the bells that still can ringForget the perfect offeringThere is a crack in everythingThat's how the light gets in
-- Leonard Cohen--Lee A. Hart